Among the most difficult types of wounds to treat are those characterized by the presence of infection, devitalized tissue and/or foreign-body contamination. Currently systemic antibiotic therapy by intravenous or intramuscular injection is the clinically accepted standard for the prevention and treatment of infected surgical and traumatic wounds. Systemic administration of antibiotics is recognized as an inherently inefficient method for delivering drugs because only a small fraction of the total dose actually reaches the target area, and most of the drug is excreted unused. Additional drawbacks associated with systemic antibiotic therapy include; 1) the necessity to dose repeatedly at frequent intervals, 2) poor penetration of the antibiotic into ischemic tissue, 3) emergence of resistant bacterial strains from prolonged exposure to the drug, and 4) an increased risk of adverse side-effects because of the relatively high circulating levels of the drug. All of these disadvantages would be overcome by the development of a technique for delivering drugs directly to the target site in a form which will allow release of the drug over an extended time period. Since such a method would concentrate the drug directly where it is needed, only a small fraction of the dose would enter the systemic circulation of the patient.
Recently microencapsulated antibiotics have been developed. The local application of such encapsulated antibiotics to traumatic and surgical wounds has been described in copending U.S. patent application Ser. No. 07/493,597, filed Mar. 15, 1990, which is incorporated herein by reference in its entirety. The '597 patent application describes the preparation of antibiotics encapsulated in biodegradable polymers based on lactic and/or glycolic acids and their use. The patent application further describes methods for introducing microencapsulated antibiotics into wounds by either injecting microcapsules suspended in a carrier into the wound or by layering the microencapsulated antibiotics on the wound. For maximum effectiveness it is desirable or even essential for the microcapsules be distributed as evenly as possible in/on the wound site. Uneven drug distribution may result in treatment failure since some areas may remain untreated. Animal studies have shown that the efficacy of therapy with microencapsulated drugs is dependent to a large extent on the ability to achieve a uniform distribution of the microspheres throughout the wound site.
The injection route is suitable only for introducing material into the limited area which the needle can traverse. The layering technique has presented difficulties because the microcapsules have shown a tendency to clump, which has made it necessary to manually spread the capsules over the site. When the microspheres clump together it has been found to interfere with the desired timed release of the active agent. Shaker-type applicators, dispensing from pipets and other methods have not afforded an easy method for obtaining the required distribution.
It has become apparent that an easier and more accurate method is needed for implanting or spreading the microcapsules.